As digital devices including computers have become more advanced, digital content (hereafter simply referred to as content) of such as music and images has come to be handled.
Generally, content is stored in a directory structure on a storage unit arranged internal or external to a digital device. Content can be attached with additional information such as its name, recording date, and information indicative whether the content is read only or not.
Executing a predetermined program, the personal computer can easily execute content retrieval, movement, and copy for example. For example, Internet Explorer (trademark) (produced by Microsoft Corporation) displays content in a tree structure. If plural digital devices are connected to the personal computer which executes Internet Explorer, it can display all content stored in all the connected devices.
Internet Explorer displays types of content with icons. Also, when an icon representing a particular piece of content has been dragged and dropped, Internet Explorer copies or moves that content accordingly.
Thus, the content movement and copy operations can be executed easily, thereby causing problems associated with content copyright protection.
To solve the problems, copyright protection technologies are used by which content is encrypted and content usage conditions and a content key for content encryption (or decryption) are attached to the encrypted content.
The content usage conditions include reproduction count, reproduction period, movement count, copy count, and checkout count for example. The copyright protection technologies become available only when the encrypted content attached with its usage conditions and content key and a device compatible with a particular copyright protection technology are ready for use.
One of the problems involved in the related art is that copyright-protected content cannot be moved or copied unless a procedure based on a particular copyright protection technology is followed. The related-art technologies are unable to move or copy any copyright-protected content without requiring users to execute cumbersome operations.
Another problem is that, as the number of content handling devices and the volume of content increases, it becomes more difficult for users to retrieve desired pieces of content.